Study of a possible reaction pathway in the polymorphic transformation of diacetamide

A possible reaction path for the polymorphic transformation of trans‐trans solid diacetamide into its trans‐cis from is envisaged. A description of the two crystalline forms in the same crystallographic system is adopted, and the energy profile of the crystallographic reaction path is calculated by using an empirical 6‐exp. atom‐atom potential method and a 6‐13G ab initio procedure for the inter‐ and intramolecular contributions, respectively. Two barriers appear along the reaction path. The first corresponds to the destruction of the trans‐trans chains and the second to the formation of the trans‐cis dimers. These barriers, being lower than the acetyl rotation barier, are in agreement with the ability to isomerize diacetamide in solid state. The presence of a small energy minimum between these barriers would suggest the existence of an intermediate crystallographic form.